Of the reactions below, which one is a double-replacement reaction?

a. nh4cl -> nh3 + hcl
b. 2 mg + o2 -> 2 mgo
c. 2 n2 + 3 h2 -> 2 nh3
d. cd(no3)2 + na2s -> cds + 2 nano3

Answer;

D. Cd(NO3)2 + Na2S -> CdS + 2 NaNO3

Explanation;A double displacement reaction is a type of chemical reaction that takes place when two compounds reacts, and the positively charged ions or cations and the negatively charged ions or anions of the two reactants switch places resulting to the formation of two new compounds.In this case; the reaction Cd(NO3)2 + Na2S -> CdS + 2 NaNO3; is an example of double displacement reaction, in which Cd2+ ions in Cd(NO3)2 switch places with Na+, while NO3- in Cd(NO3)2 switch places with S^2- in Na2S, to form two new compounds CdS and  NaNO3.

The answer is c. valence electrons

I’m not sure what your trying to say here.. can you clarify again?